It is sure nice having a dually, it's rock steady even without a sway bar. Only issue is I now am up one level on Mexican toll roads which charge by the axle. (dually counts as 2)
I would only put the truck in 4WD if I was at risk of getting stuck. I do not use 4WD much. 2 years ago I used it in a slightly muddy area in Mexico. I then drove 60 MPH on the toll roads for 200 miles and forgot to take it out. I I was noticing my mileage was down and when I pulled to the side for my dog to pee, i saw fluid over the the inside front wheel wells. I then realized it was shooting out the top of the vent in the transfer case due to overheating. Fortunately I was just outside Navajoa where there is a GM dealer. they put it up on the hoist inspected it, topped it up and sent me on my way, never had an issue since. The charge? Zero. Heck i can't even cross the entrance of the driveway to the GM dealer here without them charging me 100 bucks. They even pressure washed the fluid off the wheel wells.
Since then I avoid 4WD or remind my wife to remind me I engaged it.